Optical device

ABSTRACT

An optical device includes: a sealed container having edge walls facing each other in a thickness direction of the container and a side wall connecting both of the edge walls; a first liquid with polarity or electrical conductivity and sealed within the container; a second liquid that is sealed within the container and does not mix with the first liquid; and a voltage applying unit for applying a voltage across the first liquid. The first liquid and the second liquid have equal specific gravity, and transmissivity of the first liquid is lower than the transmissivity of the second liquid. An interface between the first liquid and the second liquid changes shape in response to a voltage applied by the voltage applying unit. A light transmission path that passes through the edge walls and extends in a direction of the thickness of the container is formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical device.

2. Description of Related Art

An optical device that adjusts the amount of light to be transmitted bymeans of electrocapillarity (electrowetting) is proposed (For example,see Japanese Patent Application Publication No. 2001-228307).

Such an optical device 10 includes, as shown in FIG. 12A, a sealedcontainer 16 that includes edge walls 12 that face each other in thedirection of the thickness of the container 16 and a side wall 14 thatconnects both of the edge walls 12, a first liquid 20 having polarity orelectrical conductivity that is sealed within the container 16, and asecond liquid 22 that is sealed within the container 16 and that has ahigher transmissivity than the first liquid 20.

Liquids having such properties that they do not mix with each other areused as the first liquid 20 and the second liquid 22, and further,liquids having the same specific gravity are used as the first liquid 20and the second liquid 22, so that when only the first liquid 20 and thesecond liquid 22 are sealed within the container 16 without getting airor the like mixed therein, the initial state in which only the firstliquid 20 and the second liquid 22 were sealed within the container 16is maintained even if the container 16 is rotated or shaken, and a statewhere an interface 24 is roughly parallel to the edge walls 12 ismaintained.

Reference numerals 28 in the drawing is an electrode for applying avoltage across the first liquid 20, and reference numerals 30 is aninsulation film covering the electrode 28.

By applying a voltage across the first liquid 20 with theabove-mentioned electrode 28, the shape of the interface 24 between thefirst liquid 20 and the second liquid 22 is altered between the gapshown with the solid line and the broken line in FIG. 12A due toelectrocapillarity, and thus, a light transmission path 18 that passesthrough the edge walls 12 and extends in the direction of the thicknessof the container 16 is formed.

Specifically, in a state where no voltage is applied, by having thefirst liquid 20 extend, as indicated by the solid line in FIG. 12A, overthe entire area in a direction that is orthogonal to the direction inwhich light is transmitted, transmission of light is prevented orsuppressed, and as the applied voltage is increased, the transmissionpath 18 is formed by having the second liquid 22 come into contact withboth of the edge walls 12 as indicated by the broken line in FIG. 12A,and the size of the transmission path 18 is adjusted by adjusting theapplied voltage, thereby increasing or decreasing the contact areabetween the second liquid 22 and one of the edge walls 12.

SUMMARY OF THE INVENTION

In such a optical device 10 in related art, a water-repellant film 26for making the movement of the first and second liquids 20 and 22 smoothare formed on the inner side of the side wall 14. The angle of contact θformed between the first liquid 20 and the water-repellant films 26 isdetermined by the properties of the two, and the angle of contact θ issmaller than 90 degrees.

As shown in FIG. 12B, as the dimensions of the optical device 10 isreduced along the direction of light transmission (the dimension in thedirection of its thickness), while it may be possible to block the lighttransmission path 18 by having the first liquid 20, in a state where novoltage is applied, extend along the entire area in a directionorthogonal to the direction of light transmission, cases may arise wherethe light transmission path 18 cannot be formed since the second liquid22 can only come into contact with one of the edge walls 12, as shown inFIG. 12C, in a state where some voltage is applied.

Such an occurrence is due to the fact that the angle of contact θ formedbetween the first liquid 20 and the water-repellant film 26 is of avalue smaller then 90 degrees and to the fact that the interface 24forms a curved convex surface (including a spherical surface) thatcurves out from the first liquid 20 toward the second liquid 22 in thethickness direction.

Thus, conventionally, there is a limit in terms of the miniaturizationof the dimension of the optical device 10, which adjusts by means ofelectrocapillarity (electrowetting) the amount of light to betransmitted, in the direction in which light is transmitted (thedimension in the thickness direction).

On the other hand, miniaturization of imaging devices into which suchoptical devices 10 are incorporated is sought after, and how to achieveminiaturization of the dimension of the optical device 10 in thedirection in which light is transmitted (the dimension in the directionof its thickness) is becoming an important issue.

The present invention is made in view of such circumstances, and seeksto provide an optical device that is advantageous in advancingminiaturization.

According to an embodiment of the present invention, there is providedan optical device including: a sealed container that has edge walls anda side wall, the edge walls facing each other in a thickness directionof the container, the side wall connecting both of the edge walls; afirst liquid that has polarity or electrical conductivity, the firstliquid being sealed within the container; a second liquid that is sealedwithin the container and does not mix with the first liquid; and avoltage applying unit for applying a voltage across the first liquid.The first liquid and the second liquid have equal specific gravity, andtransmissivity of the first liquid is lower than the transmissivity ofthe second liquid. Furthermore, an interface between the first liquidand the second liquid changes shape in response to a voltage applied bythe voltage applying unit. Furthermore, a light transmission path thatpasses through the edge walls and extends in a direction of thethickness of the container is formed. Furthermore, a hydrophilic filmthat is formed on a portion inside the side wall corresponding to thefirst liquid, wettability of the hydrophilic film with respect to thefirst liquid being higher than wettability of the hydrophilic film withrespect to the second liquid. Furthermore, a water-repellant film thatis formed on a portion inside the side wall corresponding to the secondliquid, wettability of the water-repellant film with respect to thesecond liquid being higher than wettability of the water-repellant filmwith respect to the first liquid.

According to the present invention, when no voltage is applied, theinterface between the first and second liquids is flat. Accordingly,even if the dimension of the optical device is reduced in the directionin which light is transmitted, it is possible, unlike the opticaldevices in the related art, to reliably bring the second liquid intocontact with both of the edge walls in a state where a voltage isapplied.

Accordingly, it is possible to reliably form a light transmission pathin a state where a voltage is applied, and is thus advantageous inobtaining smaller and thinner optical devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view indicating the configuration of an opticaldevice in an embodiment of the present invention;

FIGS. 2A and 2B illustrate the principles of electrocapillarity, whereFIG. 2A shows a state before applying a voltage and FIG. 2B shows astate after a voltage is applied;

FIG. 3 illustrates a state where no voltage is applied to an opticaldevice;

FIG. 4 illustrates a state where a first voltage E1 is applied to anoptical device;

FIG. 5 illustrates a state where a second voltage E2 of a greater valuethan the first voltage E1 is applied to an optical device;

FIG. 6 illustrates a state where a third voltage E3 of a greater valuethan the second voltage E2 is applied to an optical device;

FIG. 7 is a line graph indicating the mixing ratio of pure water andethanol and the specific gravity and refractive index propertiesthereof;

FIG. 8 is a line graph indicating the mixing ratio of pure water andethylene glycol and the specific gravity and refractive index propertiesthereof;

FIG. 9 is a graph indicating the specific gravity and refractive indexof pure water, ethanol and ethylene glycol;

FIG. 10 is a graph indicating the specific gravity and refractive indexof various kinds of liquids;

FIG. 11 is a table indicating the values of specific gravity andrefractive index of various kinds of liquids used; and

FIGS. 12A, 12B and 12C indicate the configuration of an optical deviceof related art, where FIG. 12A is a diagram indicating a configurationin which ample thickness is secured for a container, FIG. 12B is adiagram indicating a state where a light transmission path is blocked ina case where the dimension of a container in the thickness direction isreduced, and FIG. 12C is a diagram indicating a state where a lighttransmission path cannot be formed in a case where the dimension of thecontainer in the thickness direction is reduced.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The issues discussed above are addressed by forming a hydrophilic filmon a portion of the inner surface of the side wall of the containercorresponding to the first liquid and by forming a water-repellant filmon a portion of the inner surface of the side wall of the containercorresponding to the second liquid.

Next, an embodiment of the present invention will be described withreference to the drawings.

First, the principles of electrocapillarity (electrowetting) that ismade use of in the optical device of the present invention will bedescribed.

FIGS. 2A and 2B illustrate the principles of electrocapillarity. FIG. 2Ashows a state before a voltage is applied, and FIG. 2B shows a stateafter a voltage is applied.

As shown in FIG. 2A, a first electrode 2 is formed on the surface of asubstrate 1, and an insulation film 3 is formed on the surface of thiselectrode 2.

On the surface of this insulation film 3 is located a first liquid 4that possesses polarity or electrical conductivity, and a secondelectrode 5 is electrically connected to the first liquid 4.

As shown in FIG. 2A, in a state where a voltage E is not applied acrossthe first electrode 2 and the second electrode 5, the surface of thefirst liquid 4 forms an approximately spherical shape arching upward dueto surface tension. At this point, the angle θ formed between thesurface of the insulation film 3 and the liquid surface where the firstliquid 4 is in contact with the insulation film 3, in other words theangle of contact θ, is taken to be θ0.

However, as shown in FIG. 2B, when the voltage E is applied across thefirst electrode 2 and the second electrode 5, an electrical field(electrostatic force) affects the particles constituting the firstliquid 4 as a build-up of, for example, positive charge takes place onthe surface of the insulation film 3. Thus, particles constituting thefirst liquid 4 are attracted, the wettability of the first liquid 4 withrespect to the insulation film 3 improves, and the angle of contact θbecomes θ1, which is smaller than θ0. Further, the angle of contact θbecomes smaller as the value of voltage E increases.

This is called electrocapillarity.

Next, an optical device 40 of the present embodiment will be described.

FIG. 1 is a sectional view indicating the configuration of the opticaldevice 40 in the present embodiment.

As shown in FIG. 1, the optical device 40 includes a container 42, afirst liquid 44, a second liquid 46 and a voltage applying unit.

The container 42 includes edge walls 4202 that face each other in thedirection of the thickness of the container 42, a side wall 4204 thatconnects both of the edge walls 4202, and a receptacle space 42A that issealed by these edge walls 4202 and side wall 4204.

In the present embodiment, the edge walls 4202 take on the form ofdisk-like plates, the side wall 4204 takes on the form of a hollowcylinder having the same outer diameter as the outer diameter of theedge walls 4202, and the receptacle space 42A takes on the form of aflat cylinder.

In addition, the edge walls 4202 and the side wall 4204 are made ofinsulative materials, and the edge walls 4202 are made of a transparentmaterial that allows the transmission of light.

As materials for the edge walls 4202, for example, synthetic resinmaterials that are transparent and have insulative properties, ortransparent glass materials may be used.

On the inside of the side wall 4204 is formed in the shape of a hollowcylinder a first electrode 48 (negative electrode) that extends alongthe entire circumference of the side wall 4204, and on the entirecircumference of the inside of the first electrode 48 is formed in theshape of a hollow cylinder an insulation film 50 so as to cover all ofthe first electrode 48.

On a place on the inner surface of one of the two edge walls 4204 andtoward its outer circumference is formed a second electrode 52 (positiveelectrode) that extends in the shape of a ring that is concentric withthis edge wall 4204. The second electrode 52 exposes part of its innercircumference in the receptacle space 42A, and the second electrode 52is insulated from the first electrode 48 by the insulation film 50.

On a place on the inner surface of one of the two edge walls 4204 andover the entire area within the second electrode 50 is formed atransparent hydrophilic film 54 that allows transmission of light. Thehydrophilic film 54 is so formed that its wettability with respect tothe first liquid 44 is higher than its wettability with respect to thesecond liquid 46.

A power source 56 with a variable output voltage is provided on theoutside of the container 42. The negative voltage output terminal of thepower source 56 is electrically connected to the first electrode 48, andthe positive voltage output terminal of the power source 56 iselectrically connected to the second electrode 52.

In the present embodiment, the above-mentioned voltage applying unit mayinclude the first electrode 48, the second electrode 52 and the powersource 56.

The first liquid 44 has polarity or electrical conductivity, and issealed within the container 42.

The second liquid 46 does not mix with the first liquid 44 and is sealedwithin the container 42.

In addition, the first liquid 44 and the second liquid 46 have equalspecific gravity, and the first liquid 44 is such that itstransmissivity is lower than the transmissivity of the second liquid 46.

The first liquid 44 and the second liquid 46 will be described in detaillater.

On a portion on the inside of the side wall 4204 corresponding to thefirst liquid 44 is formed a hydrophilic film 58, and on a portion on theinside of the side wall 4204 corresponding to the second liquid 46 isformed a water-repellant film 60.

The hydrophilic film 58 is so configured that its wettability withrespect to the first liquid 44 is higher than its wettability withrespect to the second liquid 46. In other words, the hydrophilic film 58is so configured that the angle of contact of the first liquid 44 inrelation to the hydrophilic film 58 would be smaller than the angle ofcontact of the second liquid 46 in relation to the hydrophilic film 58.

The hydrophilic film 58 may be formed by, for example, applying ahydrophilic polymer or a surfactant on the inner surface of the sidewall 4204, and various known materials may be used to this end.

The water-repellant film 60 is so configured that its wettability withrespect to the second liquid 46 is higher than its wettability withrespect to the first liquid 44. In other words, the water-repellant film60 is so configured that the angle of contact of the second liquid 46 inrelation to the water-repellant film 60 would be smaller than the angleof contact of the first liquid 44 in relation to the water-repellantfilm 60.

The water-repellant film 60 may be formed by applying, for example, awater-repellant agent of fluoride compounds and the like on the innersurface of the side wall 4204, and various known materials may be usedto this end.

First, the second liquid 46 is injected into the receptacle space 42A ofthe container 42 and onto the edge wall 4202 on the side on which thewater-repellant film 60 is provided, so that its fluid level is at theupper edge of the water-repellant film 60. Then, the first liquid 44 isinjected thereonto, and the second liquid 46 and the first liquid 44 aresealed within the receptacle space 42A by taking out the air inside.

Thus, the entire area of the first liquid 44 located at the entire outercircumference of the inner surface of the edge wall 4202 where the firstliquid 44 is located becomes electrically connected to the secondelectrode 52 by coming into contact therewith, and further, the entirearea of the first liquid 44 located at the entire outer circumference ofthe receptacle space 42A faces the first electrode 48 with theinsulation film 50, the hydrophilic film 58 and the water-repellant film60 in-between.

Therefore, when a voltage is applied across the first electrode 48 andthe second electrode 52 by the power source 56, a voltage is appliedacross the first liquid 44.

Next, operations of the optical device 40 will be described.

FIG. 3 illustrates a state where no voltage is applied to the opticaldevice 40, FIG. 4 illustrates a state where a first voltage E1 isapplied to the optical device 40, FIG. 5 illustrates a state where asecond voltage E2 of a value greater than the first voltage E1 isapplied to the optical device 40, and FIG. 6 illustrates a state where athird voltage E3 of a value greater than the second voltage E2 isapplied to the optical device 40.

In a state where no voltage is applied across the first electrode 48 andthe second electrode 52 from the power source 56 (E=0V), as shown inFIG. 3, the entire area of the first liquid 44 located at the entireouter circumference of the receptacle space 42A is in contact with thesurface of the hydrophilic film 58, the angle of contact thereof is 90degrees, the entire area of the second liquid 46 located at the entireouter circumference of the receptacle space 42A is in contact with thesurface of the water-repellant film 60, and the angle of contact thereofis 90 degrees.

Therefore, an interface 62 formed between the first liquid 44 and thesecond liquid 46 is flat.

At this point, since the first liquid 44 extends across an entire areain a direction that is orthogonal to the direction in which light istransmitted, light that travels in the direction of the thickness of thecontainer 42 is blocked.

When the first voltage E1 is applied across the first electrode 48 andthe second electrode 52 from the power source 56 (where E1>0V), as shownin FIG. 4, due to electrocapillarity, the interface 62 changes its shapeinto a convex curved surface (spherical surface) that arches outwardfrom the second liquid 46 toward the first liquid 44 such that thecenter of the interface 62 is now closer to one of the edge walls 4202.In other words, the thickness of the first liquid 44 is smallest(thinnest) at the center, and its thickness becomes greater (thicker)the further away it moves from the center toward the outer circumferenceof the receptacle space 42A.

At this point, the angle of contact of the first liquid 44 with respectto the water-repellant film 60 is smaller than 90 degrees, and at theside wall 4204 (the water-repellant film 60), the first liquid 44 entersthe second liquid 46 along the side wall 4204.

When the second voltage E2 of a value greater than the first voltage E1is applied across the first electrode 48 and the second electrode 52from the power source 56 (where E2>E1), as shown in FIG. 5, the gradientof the convex curved surface (spherical surface) of the interface 62becomes greater, and the center of the interface 62 touches one of theedge walls 4202 (the hydrophilic film 54).

As a result, the first liquid 44 ceases to be present on the edge wall4202 (the hydrophilic film 54) where the interface 62 is in contactwith, an area 64 where only the second liquid 46 is present is formed inthe center of the receptacle area 42A (the center of both of the edgewalls 4202), and a light transmission path 66 that passes through theedge walls 4202 and extends in the direction of the thickness of thecontainer 42 is formed by way of this area 64.

When the third voltage E3 of a value greater than the second voltage E2is applied across the first electrode 48 and the second electrode 52from the power source 56 (where E3>E2), as shown in FIG. 6, the gradientof the convex curved surface (spherical surface) of the interface 62becomes even greater.

The diameter of the area 64 formed in the center of the receptacle space42A (the center of both of the edge walls 4202) where only the secondliquid 46 is present is enlarged, and the diameter of the lighttransmission path 66 is enlarged.

Thus, by adjusting the voltage applied across the first electrode 48 andthe second electrode 52 from the power source 56, it is possible toenlarge or reduce the diameter of the area 64 where only the secondliquid 46 is present, and it is possible to perform aperture operationswhereby the diameter of the light transmission path 66 is enlarged orreduced.

According to the present embodiment, when no voltage is applied, theangle of contact θ of the first liquid 44 with respect to thehydrophilic film 58 and to the water-repellant film 60 is 90 degrees,the angle of contact of the second liquid 46 with respect to thehydrophilic film 46 and to the water-repellant film 58 is 90 degrees,and the interface 62 is flat. Therefore, even if the dimension of theoptical device 40 in the direction in which light is transmitted (thedimension in the direction of its thickness) is reduced, unlikeconventional optical devices, it is possible to bring the second liquid46 into contact with both of the edge walls 4202 reliably in a statewhere a voltage is applied.

Therefore, the light transmission path 66 can be formed reliably in astate where a voltage is applied, and it is advantageous in obtainingthinner devices.

If, as is conventional, the interface 62 between the first and secondliquids 44 and 46 takes on the form of a concave curved surface wherethe first liquid 44 curves out toward the second liquid 46 (see FIG.12A), a situation arises where the second liquid 46 exists between thefirst liquid 44 and the first electrode 48, and therefore, since thevoltage applied via the first electrode 48 is obstructed by the secondliquid 46, it becomes more difficult to apply a voltage across the firstliquid 44, electrocapillarity in the first liquid 44 cannot be broughtabout reliably, and it is disadvantageous in stabilizing apertureoperations.

In contrast, in the present embodiment, since the interface 62 betweenthe first and second liquids 44 and 46 is flat, the second liquid 46never exists between the first liquid 44 and the first electrode 48.Therefore, the voltage applied via the first electrode 48 is appliedacross the first liquid 44 without being obstructed by the second liquid46, and thus, electrocapillarity in the first liquid 44 can be broughtabout reliably, and it is advantageous in stabilizing apertureoperations.

In addition, since the water-repellant film 60 is formed on the portionof the side wall 4204 corresponding to the second liquid 46, if thefirst liquid 44 comes to where the water-repellant film 60 is, thesurface of the first liquid 44 moves smoothly over the water-repellantfilm 60, and it is advantageous in achieving faster aperture operations.

In addition, since the hydrophilic film 54 is formed on the edge wall4202 on the side of the first liquid 44, the hydrophilic film 54 is verywettable with respect to the first liquid 44. Therefore, when the secondliquid 46 moves away from the edge wall 4202 on the side of the firstliquid 44 after having been in contact with that edge wall 4202, it iseasier for the second liquid 46 to detach from the hydrophilic film 54,and it is advantageous in achieving faster aperture operations.

Next, the first liquid 44 and the second liquid 46 used in theembodiment above will be described.

The first liquid 44 is obtained by mixing three kinds of liquids eachhaving a specific gravity and refractive index that are different fromthose of one another, and the present inventor discovered the fact thatthe specific gravity and refractive index of the first liquid 44 can bechanged over a large range by changing the mixing ratio of these threekinds of liquids.

As an example, a case where the first liquid 44 is obtained by mixingtwo kinds of liquids will first be described.

The first liquid 44 will be obtained by mixing pure water and ethanol asthe two kinds of liquids, and the mixing ratio thereof will be varied.

As shown in FIG. 7, as the mixing ratio of these liquids is varied, thespecific gravity and refractive index of the first liquid 44 changeslinearly or in a curve.

In addition, the first liquid 44 will be obtained by mixing pure waterand ethylene glycol as the two kinds of liquids, and the mixing ratiothereof will be altered.

As shown in FIG. 8, as the mixing ratio of these liquids is varied, thespecific gravity and refractive index of the first liquid 44 changeslinearly or in a curve.

It is noted that the specific gravity and refractive index of pure waterare 1.0 and 1.333, respectively, that the specific gravity andrefractive index of ethanol are 0.789 and 1.361, respectively, and thatthe specific gravity and refractive index of ethylene glycol are 1.113and 1.430, respectively.

In contrast to the examples above, the first liquid 44 is next obtainedby mixing three kinds of liquids, and the mixing ratio thereof isvaried.

As an example, the first liquid 44 is obtained using pure water, ethanoland ethylene glycol as the three kinds of liquids, and the mixing ratiothereof is varied.

As shown in FIG. 9, by varying the mixing ratio of pure water, ethanoland ethylene glycol, it is possible to alter the specific gravity andrefractive index of the first liquid 44 over a large range R that isobtained by joining the three coordinates for pure water, ethanol andethylene glycol.

On the other hand, in FIG. 9, coordinates of the specific gravity andrefractive index of various silicone oils that are commerciallyavailable are indicated.

Therefore, a commercially available silicone oil that falls within thetriangular area R may be used as the second liquid 46, and the firstliquid 44, which is obtained by mixing pure water, ethanol and ethyleneglycol and whose specific gravity and refractive index are made equal tothose of the silicone oil above, may be used.

In the present embodiment, the first liquid 44 is formed by dissolvingcarbon black in a mixture of pure water, ethanol and ethylene glycol,has a black color, is so formed that it can block light with a thicknessof approximately 0.1 mm, and is advantageous in obtaining thinneroptical devices.

By making the refractive index of the first liquid 44 and the refractiveindex of the second liquid 46 equal, occurrences of a lens effect at theinterface 62 can be prevented, and it is advantageous in improving thereliability of aperture operations.

In addition, by forming the first liquid 44 by mixing ethanol in water,its freezing-point (melting-point) can be lowered, freezing in coldclimates can be prevented, and the use of the optical device 40 in coldclimates becomes possible.

In the present embodiment, the freezing-point of ethanol is −114 degreesCelsius, the freezing-point of ethylene glycol is −13 degrees Celsius,and it is possible to keep the freezing-point of the first liquid 44 at40 degrees Celsius or below.

In addition, in the embodiment above, since three kinds of existingliquids with different values of specific gravity were mixed and used asthe first liquid 44, as indicated by the area R in FIG. 9, variationsover a wide range are possible.

In other words, when two kinds of liquids with different values ofspecific gravity are mixed, the specific gravity of the first liquid 44that can be obtained by varying the mixing ratio of those two kinds ofliquids can only be varied, as shown in FIG. 9, within the range of theline that joins the coordinates of those liquids.

In contrast, when three kinds of liquids are mixed, it becomes possibleto vary the specific gravity of the first liquid 44 within the largertriangular area R that is obtained by joining the three coordinates forpure water, ethanol and ethylene glycol.

Therefore, it is easier to make the specific gravity of the first liquid44 and the specific gravity of the second liquid 46 equal, and it iseasier to obtain the optical device 40 with the desired properties.

Further, as shown in FIG. 9, since the first liquid 44 is obtained bymixing at least three kinds of liquids, for example, pure water, ethanoland ethylene glycol, that have not only differing values of specificgravity but differing refractive indices as well, while it is easier tomake the specific gravity of the first liquid 44 and the specificgravity of the second liquid 46 equal, it is also easier to make therefractive index of the first liquid 44 and the refractive index of thesecond liquid 46 equal, and it is therefore advantageous in preventingthe occurrence of a lens effect.

In addition, in the embodiment above, a case where the first liquid 44is obtained by mixing pure water, ethanol and ethylene glycol as theseveral kinds of liquids is described, however, the several kinds ofliquids to be used are not limited to pure water, ethanol and ethyleneglycol, and various kinds of other existing liquids may also be choseninstead.

A description will be given with reference to FIG. 10 and FIG. 11.

FIG. 10 is a graph indicating the specific gravity and refractive indexof various kinds of liquids, and FIG. 11 is a graph indicating thevalues of specific gravity and refractive index of the various liquidsto be used.

For example, as shown in FIG. 10, as liquids to be used, those thatbelong to group A, group B, group C and group D may be considered, andthe actual names of liquids to be used in groups A to D are shown inFIG. 1.

As indicated with a triangular area R1 in FIG. 10, it is possible tovary the specific gravity and refractive index by varying, within thelarge triangular area R1 that is obtained by joining the coordinates ofone liquid chosen from group A, another from group B, and another fromgroup C as the three kinds of liquids, the mixing ratio of thoseliquids.

In addition, as shown with a triangular area R2 in FIG. 10, it ispossible to vary the specific gravity and refractive index by varying,within the large triangular area R2 that is obtained by joining thecoordinates of one liquid chosen from group B, another from group C, andanother from group D as the three kinds of liquids, the mixing ratio ofthose liquids.

In other words, by choosing various known liquids and changing themixing ratio thereof, it is possible to vary the specific gravity andrefractive index with ease.

It is to be noted that the number of liquids to be used for the firstliquid is not limited to three, and four or more kinds of liquids may bealso be used.

In addition, in the embodiment above, a case where the first liquid 44is so formed to be equal in specific gravity with the second liquid 46by mixing several kinds of liquids, each having a different specificgravity and refractive index, is described, however, it is also possibleto form the second liquid 46 by mixing several kinds of liquids, eachhaving a different specific gravity and refractive index, so that itsspecific gravity equals that of the first liquid 44.

Further, in the embodiment above, a case where a single silicone oil isused as the second liquid 46 is described, however, several siliconeoils that have differing properties, such as refractive index andspecific gravity, are available, and while it is possible to choose onekind of silicone oil that has the desired properties and use it as thesecond liquid 46, it is also possible to select several kinds ofsilicone oils with differing properties, vary their mixing ratio, anduse them as the second liquid 46 with the desired refractive index andspecific gravity.

In addition, in the embodiment above, a case where electrocapillarity isbrought about by applying a DC, voltage across the first liquid 44 isdescribed, however, the voltage to be applied across the first liquid 44is not limited to a DC voltage, and any kind of voltage, such as an ACvoltage, pulse voltage, a voltage that fluctuates in steps, may be usedso long as electrocapillarity can be caused in the first liquid 44.

The present document claims priority to Japanese Priority Document JP2005-063324, filed in the Japanese Patent Office on Mar. 8, 2005, theentire contents of which are incorporated herein by reference to theextent permitted by law.

Since the invention disclosed herein may be embodied in other specificforms without departing from the spirit or general characteristicsthereof, some of which forms have been indicated, the embodimentsdescribed herein are to be considered in all respects illustrative andnot restrictive. The scope of the invention is to be indicated by theappended claims, rather than by the foregoing description, and allchanges which come within the meaning and range of equivalents of theclaims are intended to be embraced therein.

1. An optical device, comprising: a sealed container that has edge wallsand a side wall, the edge walls facing each other in a thicknessdirection of the container, the side wall connecting both of the edgewalls; a first liquid that has polarity or electrical conductivity, thefirst liquid being sealed within the container; a second liquid that issealed within the container and does not mix with the first liquid; andvoltage applying means for applying a voltage across the first liquid;wherein: the first liquid and the second liquid have equal specificgravity; transmissivity of the first liquid is lower than thetransmissivity of the second liquid; an interface between the firstliquid and the second liquid changes shape in response to a voltageapplied by the voltage applying means; a light transmission path thatpasses through the edge walls and extends in a direction of thethickness of the container is formed; a hydrophilic film that is formedon a portion inside the side wall corresponding to the first liquid,wettability of the hydrophilic film with respect to the first liquidbeing higher than wettability of the hydrophilic film with respect tothe second liquid; a water-repellant film that is formed on a portioninside the side wall corresponding to the second liquid, wettability ofthe water-repellant film with respect to the second liquid being higherthan wettability of the water-repellant film with respect to the firstliquid; the voltage applying means includes a first electrode providedon an entire circumference of the inside of the side wall and a secondelectrode provided along an outer circumference of the inside of theedge wall on a side on which the first liquid is located; thehydrophilic film and the water-repellant film are provided so as tocover a surface of the first electrode; another hydrophilic film isformed on an inner portion of the second electrode and on the inside ofthe edge wall on a side on which the first liquid is located; andwettability of the another hydrophilic film with respect to the firstliquid is higher than wettability of the another hydrophilic film withrespect to the second liquid.
 2. The optical device according to claim1, wherein: the interface is formed in a plane that is orthogonal to thethickness direction of the container; the hydrophilic film is providedon a portion on the inside of the side wall corresponding to the firstliquid along an entire circumference; and the water-repellant film isprovided on a portion on the inside of the side wall corresponding tothe second liquid along an entire circumference.
 3. The optical deviceaccording to claim 1, wherein: the voltage applying means includes afirst electrode provided on an entire circumference of the inside of theside wall and a second electrode provided along an outer circumferenceof the inside of the edge wall on a side on which the first liquid islocated; and the hydrophilic film and the water-repellant film areprovided so as to cover a surface of the first electrode.
 4. An opticaldevice, comprising: a hydrophilic film between a first liquid and a sidewall; a water-repellant film between a second liquid and said side wall,said first liquid being between said second liquid and an edge wall;another hydrophilic film between said second liquid and said edge wall,said first liquid being between said another hydrophilic film and saidsecond liquid, wherein said hydrophilic film is between saidwater-repellant film and said edge wall, light being transmissiblethrough said edge wall.
 5. The optical device according to claim 4,wherein said side wall is formed in the shape of a hollow cylinder. 6.The optical device according to claim 4, wherein a container includessaid side wall and said edge wall.
 7. The optical device according toclaim 6, wherein said side wall is in contact with said edge wall andanother edge wall to seal a receptacle space of said container, saidfirst and second liquid being within said receptacle space.
 8. Theoptical device according to claim 4, wherein an insulation film isbetween said side wall and a first electrode.
 9. The optical deviceaccording to claim 8, wherein said first electrode is between said sidewall and said hydrophilic film.
 10. The optical device according toclaim 8, wherein said first electrode is between said side wall and saidwater-repellant film.
 11. The optical device according to claim 4,wherein said first liquid has polarity or electrical conductivity. 12.The optical device according to claim 4, wherein an interface betweensaid first liquid and said second liquid changes shape in response to avoltage applied across said first liquid.
 13. The optical deviceaccording to claim 4, wherein said second liquid does not mix with saidfirst liquid.
 14. The optical device according to claim 4, wherein thetransmissivity of said first liquid is lower than the transmissivity ofsaid second liquid, the specific gravity of said first and secondliquids being equal.
 15. The optical device according to claim 4,wherein said another hydrophilic film allows transmission of said light.16. The optical device according to claim 4, wherein wettability of thehydrophilic film with respect to said first liquid is higher than saidwettability of the hydrophilic film with respect to said second liquid.17. The optical device according to claim 4, wherein wettability of thewater-repellant film with respect to said second liquid is higher thansaid wettability of the water-repellant film with respect to said firstliquid.
 18. The optical device according to claim 4, wherein wettabilityof the another hydrophilic film with respect to said first liquid ishigher than said wettability of the another hydrophilic film withrespect to said second liquid.
 19. The optical device according to claim4, wherein said another hydrophilic film is on said first electrode.